• Simon Peyton Jones's avatar
    Refactor treatment of wildcards · 1e041b73
    Simon Peyton Jones authored
    This patch began as a modest refactoring of HsType and friends, to
    clarify and tidy up exactly where quantification takes place in types.
    Although initially driven by making the implementation of wildcards more
    tidy (and fixing a number of bugs), I gradually got drawn into a pretty
    big process, which I've been doing on and off for quite a long time.
    
    There is one compiler performance regression as a result of all
    this, in perf/compiler/T3064.  I still need to look into that.
    
    * The principal driving change is described in Note [HsType binders]
      in HsType.  Well worth reading!
    
    * Those data type changes drive almost everything else.  In particular
      we now statically know where
    
           (a) implicit quantification only (LHsSigType),
               e.g. in instance declaratios and SPECIALISE signatures
    
           (b) implicit quantification and wildcards (LHsSigWcType)
               can appear, e.g. in function type signatures
    
    * As part of this change, HsForAllTy is (a) simplified (no wildcards)
      and (b) split into HsForAllTy and HsQualTy.  The two contructors
      appear when and only when the correponding user-level construct
      appears.  Again see Note [HsType binders].
    
      HsExplicitFlag disappears altogether.
    
    * Other simplifications
    
         - ExprWithTySig no longer needs an ExprWithTySigOut variant
    
         - TypeSig no longer needs a PostRn name [name] field
           for wildcards
    
         - PatSynSig records a LHsSigType rather than the decomposed
           pieces
    
         - The mysterious 'GenericSig' is now 'ClassOpSig'
    
    * Renamed LHsTyVarBndrs to LHsQTyVars
    
    * There are some uninteresting knock-on changes in Haddock,
      because of the HsSyn changes
    
    I also did a bunch of loosely-related changes:
    
    * We already had type synonyms CoercionN/CoercionR for nominal and
      representational coercions.  I've added similar treatment for
    
          TcCoercionN/TcCoercionR
    
          mkWpCastN/mkWpCastN
    
      All just type synonyms but jolly useful.
    
    * I record-ised ForeignImport and ForeignExport
    
    * I improved the (poor) fix to Trac #10896, by making
      TcTyClsDecls.checkValidTyCl recover from errors, but adding a
      harmless, abstract TyCon to the envt if so.
    
    * I did some significant refactoring in RnEnv.lookupSubBndrOcc,
      for reasons that I have (embarrassingly) now totally forgotten.
      It had to do with something to do with import and export
    
    Updates haddock submodule.
    1e041b73
HsSyn.hs 4.59 KB